Switching power supply circuit

Abstract

In a switching power supply circuit including a primary side rectifying and smoothing circuit, a switching element, a converter transformer, a secondary side rectifying and smoothing circuit, and a switching element controlling section, a first primary side series resonant circuit is formed by a choke coil and a primary side series resonant capacitor, a second primary side series resonant circuit is formed by a leakage inductance occurring in a primary winding and the primary side series resonant capacitor, and a secondary side series resonant circuit is formed by a leakage inductance occurring in a secondary winding and a secondary side series resonant capacitor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority from Japanese Patent Application Nos. JP 2005-295363 filed on Oct. 7, 2005, and Japanese Patent Application No. JP 2005-296225 filed on Oct. 11, 2005, the disclosures of which are hereby incorporated by reference herein. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a switching power supply circuit. [0004] 2. Description of the Related Art [0005] As so-called soft-switching power supply of a resonant type, a current resonant type and a voltage resonant type are widely known. In a present situation, a current resonant converter of a half-bridge coupling system using two switching devices is in wide use because such a current resonant converter is easily put to practical use. [0006] However, the characteristics of a high withstand voltage switching element, for example, are now being improved, and therefore the problem of withstand voltage in pu...

AI Technical Summary

Benefits of technology

[0043] A side of the primary winding in the series connection circuit of the choke coil and the primary winding of the converter transformer is connected to the switching element, a side of the choke coil in the series connection circuit of the choke coil and the primary winding of the converter transformer is connected to the primary side rectifying and smoothing circuit, a first primary side series resonant circuit is formed having a resonance frequency governed by an inductance of the choke coil and a capacitance of the primary side series resonant capacitor, a second primary side series resonant circuit is formed having a resonance frequency governed by a leakage inductance occurring in the primary winding of the converter transformer and the capacitance of the primary side series resonant capacitor, and a secondary side series resonant circuit is formed having a resonance frequency governed by a leakage inductance occurring in the secondary winding of the converter transformer and capacitance of the secondary side series resonant capacitor, the resonance frequency of the first primary side series resonant circuit, the resonance frequency of the second primary side series resonant circuit, and the resonance frequency of the secondary side series resonant circuit are set substantially equal to each other. Therefore, a variable frequency range of the switching frequency of the switching element can be narrowed.

[0045] Thus, the switching power supply circuit having the series resonant circuit on the secondary side according to the embodiment of the present invention eliminates the abnormal operation in which ZVS (Zero Voltage Switching) operation is not obtained in a load condition range of intermediate load.

[0046] In addition, since the current flowing from the smoothing capacitor of the rectifying and smoothing circuit generating the rectified and smoothed voltage (direct-current input voltage) from the commercial alternating-current power into the switching converter is a direct current, a small value is selected for the capacitance of a part element as the smoothing capacitor, and a general-purpose product can be selected. Thus, effects of reducing cost and decreasing size of the smoothing capacitor, for example, are obtained.

[0047] In addition, a characteristic of total power conversion efficiency can be improved greatly by reducing a power loss according to a reduction in the amount of current flowing within the power supply circuit. Further, the voltage of the switching element is clamped by the series circuit of the clamping capacitor and the auxiliary switch element, so that the withstand voltage of the switching element can be lowered.

Problems solved by technology

This operation is an abnormal operation in which ZVS is not properly performed.

That is, it is known that a voltage resonant converter provided with a secondary side series resonant circuit as shown in FIG. 17 causes the abnormal operation in which ZVS is not properly performed at the time of the intermediate load.

However, as shown by the switching current IQ1 in FIG. 19B, a considerable peak current flows at the time of turning on the switching element Q1, thereby inviting an increase in switching loss and constituting a factor in lowering power conversion efficiency.

At any rate, an abnormal operation as described above causes a shift in phase-gain characteristics of a constant-voltage control circuit system, for example, thus resulting in a switching operation in a state of abnormal oscillation.

Thus, in the present situation, it is generally recognized to be difficult to put the power supply circuit of FIG. 17 to practical use in actuality.

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